M.B.Doc/1999 E320 Crank Position Sensor
 

After my original post on this subject, a poster said it was a diy project. I couldn't remember if I had our local German car shop replace it or not so I called and found out it hadn't been replaced. They said MB would have to do it because of resetting something they did not have the scanner/tool for. Does this sound right or is it indeed a diy job?? Thanks!!

yes that is right you need a scan tool to do it properly. an alternative is to R+R it and let the computer learn and adapt to the sensor

Yes, this is mysterious.

WIS indeed calls for resetting something when replacing CPS, but lots of folks (me included) haven't and have had no problems.

Nevertheless, you should appreciate your mechanic for following factory procedures.

What kind of problems are you haveing.. Most CPS's when they fail cause problems with stalling or dieing when hot.

Changing it out is no big deal one bolt and a few minutes. No need to reset anything your car will learn...

M.B. Doc/199 E320
 

Chris, the problem is that it does stall, sometimes when cold and sometimes after driving 10-15 miles on the highway as you stop/slow for a turn or traffic light. The last couple of times we drove it, once approximately 35 miles straight, mostly @ hiway speeds and the other times just around town, it has run perfect with no hint at shutting off. It has been in the shop for other work and scanned but gives no codes. The shop owner said it needed to be done by a dealer so they could scan/reset the new unit, all for only $421---so now you see why I am starting to wonder if I really need to have them do it or do it myself and let/hope it resets on it's own. That price seems high since it has only the one bolt and especially if it will indeed reset itself.

you could r+r the sensor and drive the car and see how it performs

Hey y'all,
Not sure if I should start another thread or not. This is a cps question, but different model. 1988 300SE. I think there are two CPS's, one front- one rear. How do you figure out which one (or both) is causing problems? Thanx for all the great info. This site is awesome....

The front is camshaft postion sensor
The rear is crankshaft position sensor

I had an '88 300TE (same engine as yours) on which the wiring to the camshaft position sensor was cut off and it made no difference.

You don't say what the problem is. If it's a hard start, rough idling, stalling type problem, it's the hefty 4-prong CPS at the back of the cylinder head. That component is actually 2 identical resistors enclosed in a single case. One resistor is for KE controller (fuel management) and the other is for EZL controller (ignition management). That sensor can be tested with an Ohmmeter by measuring on diagonal pins and the result compared to a temperature chart (look in the archives).

The front CPS is not involved in engine operation, but is used for diagnostic purposes, or so I've been told. It supplies the so-called TD signal to the X11 diagnostic connector.

[QUOTE=Cal Learner;... it's the hefty 4-prong CPS at the back of the cylinder head. ..

That is the temp Thermistor sensor .. NOT CPS.

CPS is a Hall Effect sensor at the flywheel and has nothing to do with 4- prong temp sensor or Thermistor resistance chart.
CPS is ECU/Ign trigger signal.

Go to parts look-up on top of page.

Crank Position Sensor.

Thanx for the reply Cal,
When you say "4-prong CPS at the back of the cylinder head", do you mean that component is actually attached to the back of the cylinder head, or is this something located behind the firewall in the vicinity of and kinda behind the cylinder head. I have nothing matching your description attached to the back of cyl. head. "The Problem" -- Yesterday eve. when I tried to start my car (1988 300 SE ) I immediately heard a sort of backfire I think. The engine would crank over strong, but not start. After continueosly trying ( and I must say that 18 month old Napa battery is a Dang good one!!!) I finally got the engine to start, but it would not idle or even run at all below 1500 RPM. I had to constantly pump the accelerator pedal to keep it running unless I had it around 2500-3000RPM. It was very erratic even then, and also felt and sounded like it had a really bad miss, running very rough. After it died it took several more tries to get it started and it would only start if I primed it with gasoline through the throttle body. After running roughly for awhile I started smelling something (electrical) burning , and it appeared to be emanating from under the dash. So I let the car die and jumped out to disconnect battery. Today all electrical accessories and dash and instruments appear to be working (can't seem to find what was burning), but of course the engine will not start. Several people,( none of which are pro mechanics) said their vehicles did basically same symptoms and changing their CPS cured the problem for them. Any info and comments would be welcome, as I am poor and this car is my only means to get to work..........Thanx in advance

Thanks Arthur for clearing that up. Do you know where this CPS is located on my vehicle? 1988 300 SE. There is nothing visible around flywheel location looking from top. Do I need to get under car to see this CPS? Would it cause my symptoms?

You may want to do a search on OVP relay.

Yikes, a senior moment. I obviously had CTS on the mind. Thanks, Arthur for the correction. Sorry to all. Of course, CPS is located at the back of the engine at the bell housing. The cable runs over to the EZL control unit on the left fender liner.

We replace 3 or 4 a week, mostly on the M112 engined late 90's cars. The scanner they are talking about reteaching rotor adaptation (along with clearing the DTC if the CPS triggered a code). Rotor adaptation should be reset whenever CPS's are changed or engine mounts are changed - it deals with incongruencies in timing due to torquing of the motor (you change relative timing just by putting a lever in the engine compartment and prying over on the engine while its running) or other effects and hiccups in timing.